The field of the invention relates to coalescers, coalescing elements, coalescing systems, coalescing methods, and coalescing media for coalescing a mixture of two phases, namely a continuous phase and a dispersed phase. In particular, the field relates to coalescers, coalescing elements, coalescing systems, coalescing methods, and coalescing media for coalescing drops of the dispersed phase in order to collect and remove the dispersed phase from the mixture.
Coalescers are used widely to remove immiscible droplets from a gaseous or liquid continuous phase, such as in crankcase ventilation (CV) filtration, fuel water separation (FWS), and oil-water separation. Prior art coalescer designs incorporate the principles of enhanced droplet capture and coalescence by utilizing graded capture (i.e., decreasing fiber diameter, pore size and/or porosity in coalescing media) or by utilizing thick depth coalescers. Wettability also is recognized as affecting coalescer performance. (See, e.g., U.S. Pat. No. 6,767,459 and U.S. published Patent Application Nos. 2007-0131235 and 2007-0062887). U.S. Pat. No. 5,443,724 discloses that the media should have a surface energy greater than water in order to improve coalescer performance (i.e., that the media should be preferentially wetted by both coalescing droplets and continuous phases). U.S. Pat. No. 4,081,373 discloses that coalescing media should be hydrophobic in order to remove water from fuel. U.S. published Patent Application No. 2006-0242933 discloses an oil-mist coalescer in which the filtration media is oleophobic, thereby enabling the fluid mist to coalesce into droplets and drain from the filtration media.
With regard to the removal of water from fuel, there is a need to increase removal efficiency and to remove smaller droplets than in the past, in order to protect high pressure rail fuel-injection systems. This challenge is further magnified by the introduction of new fuels with lower interfacial tensions and different additive packages, than fuels in the past. In fuels with lower interfacial tension, the size of dispersed drops is decreased, making the drops more difficult to remove. Enhanced coalescence therefore is needed to meet these challenges. Improved coalescers that include improved coalescing media also are desirable because they permit the use of a smaller media pack in view of improved coalescing efficiency. In fuels with lower interfacial tension, the size of drops is decreased, making the drops more difficult to remove.
In the case of fuel, high pressure common rail (HPCR) application, essentially all non-dissolved water should be removed from ultra low sulfur diesel (ULSD) fuel and biodiesel. These fuels tend to have lower interfacial tensions, therefore smaller drop size and more stable emulsions, than previous diesel fuel. In addition, the rate of coalescence between drops may be reduced by the presence of surfactants. Traditional FWS tend to be single-stage devices in which the media is phobic with respect to the dispersed phase and acts as a barrier to the dispersed phase. Traditional FWS tend not to provide adequate removal for HPCR systems, as they are intended for use upstream of a fuel pump with high interfacial tension fuels, hence, their pore size tends to be too large to effectively capture the small drops. Also, even when the mean pore size is sufficiently small, FWS media typically possess a maximum pore size great enough that excessive amounts of water passes through these large pores. Traditional two-stage fuel-water coalescers (FWC) are designed to be used downstream of the fuel pump and tend to be two-stage devices for fuel in which the first stage captures the drops, holds them so coalescence can occur, then releases the enlarged drops which are removed by sedimentation/settling, typically after being blocked by the second separator stage (where the second separator stage acts as an FWS). Traditional two-stage FWC tend to provide higher removal efficiency than FWS, but tend to have insufficient life, due to plugging by solids or semisolids. To varying degrees, both FWS and FWC are adversely affected by the presence of surfactants that lower interfacial tension, reduce drop size, slow down the rate of coalescence, stabilize emulsions, and may adsorb onto media and render it less effective. Therefore, is a need for a high efficiency, low pressure drop fuel water coalescer that is minimally affected by low interfacial tension and the presence of surfactants.
For CV applications, near 100% removal efficiency of oil mist is required to protect the turbocharger in closed CV applications and to protect the environment in open CV applications. Increasingly high efficiency, low pressure drop and longer life are sought. To accomplish this, the media should be protected from plugging, submicron droplets need to be removed, and the oil needs to drain quickly from the media.